It is customary for maintenance and inspection workers to enter the interior of industrial boilers and areas associated with these spaces to perform necessary maintenance, inspection and repairs during boiler outages.
Inspection and maintenance workers may examine boiler structure, tubing, and associated components for wear, damage or other deviations from design specifications. In general all the components are required to be observed by maintenance or inspection workers who would not otherwise be able to do so during boiler operation. Repair and maintenance may involve numerous operations such as welding, chemical treatments, and physical cleaning such as scraping, grinding and/or sandblasting. Chemical agents and cleaners may be highly toxic, and/or produce harmful or toxic fumes or vapors when used.
Welding often produces products of combustion which may be a mixture of very fine particles and gases. The fumes and gases produced during welding may arise from such things as the base materials themselves, material coatings, shielding gases, filler materials, compounds produced from environmental constituents by the heat and light mediated reactions arising from the electrical arc or high temperature flame used to weld. Many of the substances may be extremely toxic. Such things as oxides of nitrogen and ozone are gases of major toxicological importance, and incomplete oxidation may occur and carbon monoxide can form as a byproduct. In addition shielding gases such as argon may settle and displace life-supporting atmosphere.
In general, any process that produces dust particles fine enough to remain in the air long enough to be inhaled, ingested or absorbed may be regarded as hazardous. The confined spaces of the boiler and associated areas may magnify the exposure profile to airborne particles due to insufficient ventilation.
Particulate matter that builds up on the interior surfaces of the boiler during operation may become dislodged or become dispersed in the air when scraping, grinding, sandblasting or any of the numerous cleaning methods are employed. These materials may present both a long term and short term risk to the health and safety of maintenance and boiler inspection workers. It is particularly well known that abrasive blasting and other techniques such as scouring and polishing where silica flows may be used may cause rapidly progressive disease. Sandblasting creates airborne particulates generally of a silicate nature, which when breathed in are injurious to maintenance and inspection workers. Depending on the substance, such things as lung disease can occur due to accumulation of particles within the lungs or by interaction of the foreign particles with the body.
Generally, ventilation is required to keep unwanted elements at a safe level. Unwanted elements may be any or combinations of materials in various physical states, and may include gases, vapors, liquids, mists, dust, flakes, and particulates. Additionally, inadequate ventilation may allow for a deterioration of air quality wherein for example oxygen, carbon dioxide, carbon monoxide, and other substance levels may be increased or decreased to present physical uncomfort and other hazards to maintenance or inspection workers.
There are numerous laws, regulations and procedures in place with regard to air quality for workers. Boilers are often considered to be confined spaces, requiring a means to ensure that an oxygen concentration within the space is generally between 19.5% and 21.5%.
In the past, maintenance of air quality for workers within the boiler during outages has been approached by placing a fan within the opening of an access panel. This practice suffers from numerous drawbacks such as inadequate size of the opening of the access panel to incorporate a sufficient sized fan in regard to ventilation requirements, and blockage of the access panel. In addition, the requirement that workers pass through the access panel often required a setup for positioning of the fan that increased the risk for maintenance and inspection workers.
Furthermore, where boiler systems are housed within buildings or structures due to, among other things, environmental considerations, the conventional manner of providing ventilation to boiler systems may create unhealthy, unpleasant, and/or unsafe conditions within the building or housing.
Another practice has been to use the induced draft fan generally present in the system for boiler operation to cool down the boiler system. However, this type of fan must be taken out of service while workers are in the interior of the boiler system. In addition using this fan during or after cleaning with water may result in damage to air pollution control equipment.